Google to untrust WoSign and StartCom certificates

Following similar decisions by Mozilla and Apple, Google plans to reject new digital certificates issued by two certificate authorities because they violated industry rules and best practices.

The ban will go into effect in Chrome version 56, which is currently in the dev release channel, and will apply to all certificates issued by certificate authorities WoSign and StartCom after October 21. Browsers rely on digital certificates to verify the identity of websites and to establish encrypted connections with them.

Certificates issued before October 21 will continue to be trusted as long as they're published to the public Certificate Transparency logs or have been issued to a limited set of domains owned by known WoSign and StartCom customers.

The ban follows a Mozilla-led investigation that found multiple problems in the SSL certificate issuance process of WoSign, a China-based certificate authority. The investigation also revealed that in 2015 WoSign silently acquired StartCom, a CA based in Israel, without disclosing the deal to browser vendors who operate certificate root programs.

Among the issues discovered during the investigation, there were 64 cases where WoSign had issued certificates signed with the aging SHA-1 algorithm after the industry's official SHA-1 cutoff date of Jan. 1, 2016. The CA then backdated those certificates to make it appear as if they had been issued before Jan. 1, in an attempt to hide the violations.

Chinese internet security company Qihoo 360, which owns a majority stake in WoSign and implicitly in StartCom, recently stepped in and decided to separate the two CAs which had been silently sharing infrastructure, staff, policies and issuance systems for almost a year.

Qihoo 360 fired WoSign's CEO Richard Wang after it determined that he approved the backdating of 42 SHA-1 certificates issued by WoSign and two issued by StartCom. However, the company asked browser vendors to treat the WoSign and StartCom incidents separately when deciding penalties, giving the latter's long-standing history as a reliable global CA and the more limited impact of its actions.

It doesn't appear that this strategy worked, because so far Apple, Mozilla and Google announced their decisions to ban both WoSign and StartCom certificates. StartCom has been operating since 1999, being the first CA to offer free digital certificates, and unlike WoSign, most of its customers are from outside China.

"Due to a number of technical limitations and concerns, Google Chrome is unable to trust all pre-existing certificates while ensuring our users are sufficiently protected from further misissuance," said Chrome security team member Andrew Whalley in a blog post Monday. "As a result of these changes, customers of WoSign and StartCom may find their certificates no longer work in Chrome 56."

Furthermore, the exceptions for certificates issued before Oct. 21 are only temporary and are intended to give WoSign and StartCom customers time to transition to other CAs. These exceptions will be reduced in subsequent Chrome versions and the two CAs will eventually be fully untrusted.

"Sites that find themselves on this whitelist will be able to request early removal once they’ve transitioned to new certificates," Whalley said. "Any attempt by WoSign or StartCom to circumvent these controls will result in immediate and complete removal of trust."

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